In the manufacture of vehicle tires, one process operation includes disposing a cylindrical green carcass on a shaping drum and inflating the carcass to a desired generally toroidal shape. Commonly, the carcass includes inextensible beads (which include respective bead rings) adjacent each of its opposite ends. In a tire-shaping operation, the carcass is positioned about first and second generally circular mandrels with the beads engaged in air-tight sealing relationship by respective ones of the mandrels. These mandrels are mounted in spaced apart relationship on a central shaft for simultaneous movement laterally along the axis of the shaft and toward or away from one another to, among other things, permit narrowing of the axial spacing between the two mandrels, particularly in the course of radial expansion of the carcass. The mandrels of the prior art include rigid unitary mandrels and mandrels whose circumference is changeable. In those instances where the mandrels are intended to expand and retract between radially outward and inward positions, each mandrel is formed of a plurality of segments, (interchangeably referred to herein and in the art as xe2x80x9cshoesxe2x80x9d) the sum of whose radially outermost surfaces define a substantially continuous circular outer surface (circumference) which engages a respective bead ring of the carcass. The outer circumference of each mandrel commonly includes a circular elastic band or bladder (may be inflatable) disposed between the outer circumference of the mandrel and a respective bead of a green tire carcass. Once a carcass is in place about the two mandrels, the bladder may be inflated to initially form an air-tight seal between the outer circumference of each mandrel and its respective bead of the tire carcass. Thereafter, pressurized air is introduced into the region between the spaced apart mandrels to expand the tire carcass radially outwardly to shape the carcass into a tire. As the carcass is expanded, the mandrels are moved axially of the central shaft toward one another, thereby positioning the bead rings apart from one another by a distance which defines the desired width of the tire.
As noted, the two mandrels of each device need to be adjustable laterally of each other to narrow or widen the space therebetween. Initially the mandrels must be spaced apart by a distance appropriate to establish engagement of the mandrels with respective ones of the bead rings of the cylindrical carcass to thereby accept different width carcasses (for different width tires) on the same shaping drum. Thereafter, the mandrels must be moved toward one another as the carcass is radially expanded. These movements of the mandrels have been accomplished heretofore by securing each mandrel on respective opposite ends of common shaft which is provided with left and right-hand threads on opposite ones of its ends. Rotation of this shaft repositions the mandrels laterally relative to one another.
The circumferences of the two spaced apart mandrels of a shaping drum must initially be, and must remain both individually and uniformly circular and uniform in diameter (circumference) relative to one another at all positions of the mandrels along the central shaft. Failure in this respect results in non-uniformity in size and/or diameter of the rims of tires formed on such mandrels. Further, the dual mandrels must remain oriented with their respective planes normal to the longitudinal axis of the central shaft so that the mandrels remain parallel to one another, i.e., canting of a mandrel is not acceptable. Tires exhibiting the defects associated with any of these malfunctions of the mandrels must be discarded. Obviously, this results in substantial losses in time and money for the tire manufacturer.
Dimensional and spatial uniformity of the mandrel circumferences of the mandrels of prior art shaping drums generally has been a problem. In particular in the manufacture of vehicle tires of reduced width, these prior art shaping drums have been found to be substantially incapable of repetitively producing the desired dimensionally and spatially uniform rims on such reduced-width tires. In the prior art shaping drums which employ some version of a multi-segmented mandrel, control over the radial movements of the individual ones of the segments has required extensive mechanical mounting mechanisms which occupy space and limit such prior art mandrels to use in the manufacture of those tires which are wide enough to permit the interposition of the voluminous mechanical mechanisms heretofore required in these drums. This shortcoming of the prior art mandrels preludes spatial positioning of the mandrels relative to one another sufficient to allow these mandrels to accept the more narrow width tire carcasses. Mere shortening of the prior art mounting sleeves for slidably mounting of the mandrels on their central shaft has been attempted, but has resulted in unacceptable in stability of the mounting to the extent that the mandrels canted relative to the central shaft and their circumferences and/or beads could not be maintained dimensionally and/or spatially correct.
It is therefore an object of the present invention to provide a reduced width, radially adjustable, tire shaping drum.
It is another object of the present invention to provide a tire shaping drum having dual radially-adjustable mandrels which are laterally adjustable toward each other on a common shaft to a minimum separation distance between such mandrels.
It is another object to provide enhanced stability of, hence enhanced dimensional and spatial uniformity of the circumferences of, radially adjustable plural mandrels slidably disposed on a common shaft for movement toward a minimized separation distance therebetween.